For example, I don't need to load graphicx explicitly because dtklogos (which I'm using) already requires/loads it. In fact graphicx also requires/loads graphics and also keyval, which is incidentally also required/loaded by microtype. Etc. I would like to give an example involving package option conflicts, but as the relevant dependencies are cumbersome to figure out and debug, no example is on my mind right now (I've bumped into several, but since they didn't compile, I abandoned them and have forgotten about them); this is one thing this question can actually help to address.

You need to know which package loads what before hand -> There must be a list of what loads what -> There must be a central log of this -> that log should be updated -> CTAN should have that too -> ... :) option clash for xcolor
– percusseFeb 24 '13 at 14:46

@percuße There must be a way for LaTeX to automatically detect calls to \RequirePackage for it to log/write/track them somewhere else. If not, something should probably be patched; I genuinely hope that I won't need to wait for LaTeX3 :-)
– Lover of StructureFeb 24 '13 at 15:11

I think that's unfortunately pretty much wishful thinking but indeed would be nice to have. However, there are not many such cases where you would have this problem. So manual approach would almost always be easier.
– percusseFeb 24 '13 at 15:18

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\RequirePackage is everywhere yes but option clashes are rare. If some author decided to use dvipsnames and another svgnames for xcolor package, what should you do? What should be tracked? If a package requires another which requires yet enother how much deep should you go? The issue is not that straightforward to keep track of the packages AND their respective options.
– percusseFeb 24 '13 at 15:22

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If your package needs graphicx, then load it, regardless, if it is already loaded or another package loads it. Thus package dtklogo might load graphicx in it current version, but this is very likely an implementation detail for the package. In a later version dtklogos might implement it differently without graphicx and your package is then broken.
– Heiko OberdiekFeb 24 '13 at 16:04

2 Answers
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I agree with Joseph that you should always explicitly require any package that you need, regardless of whether any other package has already loaded it, but to answer your question about logging the dependency tree, one can hook into \@onefilewithoptions like so (this is better than just hooking \RequirePackage as it also hooks classes etc):

While as indicated in comments I'd recommend simply requiring those packages you use directly, the idea of a 'tree' of package dependencies has been addressed for LaTeX2e in the pkgloader package: see Automated management of package options and loading order) for more on this. As described in the package documentation, the idea is that you give the list of packages you want to use in any order and it then 'sorts out' the dependency tree.